Flexible tube pinch mechanism

ABSTRACT

A pinch mechanism suitable for use as a valve or as part of a pump. The pinch mechanism comprises a housing ( 11 ) within which an elongate conduit element ( 12 ) is located. A conduit engagement member  14  ( 13   c ) is retained within the housing ( 11 ) to be movable transverse to a longitudinal axis of the conduit element ( 12 ). The engagement member has an end portion ( 13   d ) which engages with the conduit element ( 12 ), this end portion ( 13   d ) having a cross-sectional dimension less than the lateral inner dimension of the conduit element ( 12 ), this lateral dimension being at right angles to the direction of movement of the engagement member ( 13   c ).

BACKGROUND OF THE INVENTION

[0001] This invention relates to an improved flexible tube pinchmechanism.

[0002] Pinch valves comprised of a clamp mechanism operative to clamp apiece of flexible tubing are well known. Generally a clamp or plungerwill squash the tubing flat against a surface to cut off the flow offluid through the tube. When the plunger is released flow will resumedue to pressure from the flowing fluid and (to some degree) by theelastic nature of the flexible tubing springing back into shape.

[0003] Pumps are also known which utilise a series of pinchingoperations working on a flexible tube to gradually pump fluid through ina desired direction. Such pumps and valves can be inefficient andgenerally limited in application due to the restraints of pressure orvolume throughput.

SUMMARY OF THE INVENTION

[0004] It is an object of the present invention to provide an improvedflexible tube pinch mechanism, the principles of which can be applied tovalves or pumps, the pinch mechanism exhibiting better operatingcharacteristics than known pinch mechanisms.

[0005] In a first broad aspect of the invention there is provided apinch mechanism comprising a housing adapted to receive an elongateflexible conduit element and a conduit engagement means, the engagementmeans having an engagement portion with a cross sectional dimension lessthan an inner diameter of the elongate conduit element.

[0006] In a second broad aspect of the invention there is provided apinch mechanism comprising a housing, said housing adapted to receive anelongate flexible conduit element and a conduit engagement means, theengagement means having an engagement portion with a cross sectionaldimension less than an inner diameter of the elongate conduit element,wherein said elongate conduit element is constrained within said housingto limit lateral movement thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a general perspective view of a pinch mechanismaccording to the invention,

[0008]FIG. 2 is a sectioned side elevation view of a pinch mechanismaccording to the invention in the form of a pump,

[0009]FIG. 3 is a sectioned end elevation view of the pinch mechanismrelevant to both FIGS. 1 and 2, and

[0010]FIG. 4 is an exploded view of a further form of a pumpincorporating the pinch mechanism of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011]FIG. 1 illustrates a first form of the invention, that of a pinchvalve 10. Pinch valve 10 principally includes a housing 11 (shown indotted detail in FIG. 1), extending through which is a length offlexible conduit preferably in the form of a flexible silicon tube 12.Located transverse to the longitudinal axis of tube 12 is a pistonarrangement 13. The piston arrangement includes a piston head 13 a, asealing gasket 13 b located peripherally about the piston head and aconduit engagement member in the form of plunger 13 c. Piston head 13 ais slidingly located in a cylinder bore 15 formed in housing 11. Plunger13 c is slidingly located in plunger bore 15 a which extends fromcylinder bore 15 into tube tunnel 14 in which tube 12 is located.

[0012] In use, pressure is exerted upon cylinder head 13 a by anexternal power means (such as a vacuum operated piston or anelectrically powered solenoid) to cause plunger 13 c to make contactwith and collapse tube 12 within housing 11 (as shown in FIG. 3). Thedrawing in FIG. 3 shows how the tube 12 is collapsed into a sealedclosed state, however, where only a restriction is required (say, in apump arrangement) the tube will not be fully collapsed into a sealedclosed state.

[0013] Alternatively a power means could be used to release a constantpressure on cylinder head 13 a thereby causing the plunger 13 c to beretracted from a collapsed tube 12. This will enable the tube to revertto its uncollapsed shape and permit fluid to flow therethrough.

[0014] The alternative configurations of the power means are applicableto different uses of the invention. A user can configure the pinchmechanism to be most appropriate for a given application.

[0015] To allow unhindered movement of the piston arrangement, a smallbore or passageway 20 is provided in housing 11 leading from thecylinder bore 15 to the outside atmosphere. This bore 20 serves as avent to enable piston head 13 a to move within the cylinder bore 15.

[0016] As can be seen from FIG. 1, the width of plunger 13 c is sizedsubstantially less than the outside diameter of silicon tube 12. Putanother way, the dimension of the inside of the tube at right angles tothe direction of movement of the plunger is less than thecross-sectional dimension of the plunger.

[0017] Preferably plunger 13 c has a spherical tube contacting end 13 dwhich has a diameter equal to the outside diameter of tube 12 minus fourtimes the wall thickness of tube 12.

[0018] A formula could be of the form:

D _(L) =D _(P)−4x

[0019] where D_(L) is the preferable width of plunger 13 c (thereforethe radius of plunger 13 c will be R=DL/²), D_(P) is the tube 12 outerdiameter and x is the wall thickness of tube 12.

[0020] The effect of the relative plunger 13 c dimensions is bestillustrated in FIG. 3. Plunger 13 c causes the flexible tube 12 to“invert” thereby blocking fluid flow through the fluid flow passageformed by the internal bore of tube 12. The inversion of tube 12 causesa more effective seal than conventional pinch valves which squash thetube flat against a flat surface using a plunger or clamping member of across-sectional width at least as great as the outside diameter of tube12.

[0021] Tube 12 extends through a constraining tunnel 14 in the housing11 in a close or interference fit. The nature of the tunnel 14 is suchthat no significant lateral bulging of tube 12 may occur when compressedby plunger 13 c. Tube 12 is constrained entirely within tunnel 14 andcannot expand in any direction greater than its initial outsidediameter. A tube 12 constrained in such a way has a greater “springback” characteristic and will regain its circular shape faster than aflatly pressed tube. This is especially relevant in low pressure systemswhere the fluid pressure will not aid or significantly assist in‘reinflating’ the tube 12.

[0022] A flexible tube found within a conventional pinch valve cannot beconstrained in the way described above as it requires lateral movement(unrestrained) in order to fully close. The complete inverted collapseof the “top” wall of tube 12 of the present invention onto the “bottom”wall creates what can be termed a “clown smiley face”, the mouth ofwhich is completely sealed as shown in FIG. 3.

[0023]FIG. 2 illustrates an embodiment of the invention when it is to beoperated as a pump 17. The end elevation dimensions as shown in FIG. 3remain substantially the same as the embodiment of FIG. 1 but theplunger 13 c is now in the form of an elongate pinch member 16. Thelateral width of pinch member 16 is still based on the equationconsidered above (namely, D_(L)=D_(P)−4x), however the length (as seenin FIG. 2) of pinch member 16 allows a larger section of tube 12 to beinverted at one time.

[0024] When the pinch member 16 arrangement is placed between twonon-return valve components 18 and 18 a (allowing flow only in thedirection of the arrows in FIG. 2) a pump is created which has avolumetric throughput directly proportional to the length of elongatepinch member 16. The volumetric displacement “per pump cycle” (that is,each time the tube 12 is compressed) is given by:

V=πD _(I) L+E

[0025] where V is the volume displaced, DI is the inner tube diameterand L is the length of member 16.

[0026] This is effectively the equation for a cylinder. There will,however, be a small difference created at the ends 16 a of the elongatepinch member 16 which can be measured and entered as E in the equation(which could be positive or negative). If D_(I), L and E are supplied incentimeters then the resulting V will be in milliliters. This can beconverted to a flow rate per second by multiplying it by the number ofcycles the pump completes every second.

[0027] Non-return valves 18 and 18 a could be formed by two pinch valvesas illustrated in FIG. 1. The sequence of activating each plunger withinthe valves 18 and 18 a then becomes the crucial element in maintainingthe desired direction of flow.

[0028] At the beginning of a cycle valve 18 a will be closed. When thepipe is full of fluid, valve 18 will close and valve 18 a will open.Pinch member 16 then inverts the tube 12 to pump fluid in the directionof valve 18 a.

[0029] An advantage of the present pumping method is that it may becoupled to a system with no intermediate joins. Hygienic systems such asmedical or food applications where bacteria can build up can benefitfrom simple and minimal piping connections. The pump of the presentinvention is also relevant to chemical processing as it can replaceexisting pump options where the aggressive nature of the chemical can bedamaging. Materials can be selected which resist the chemicals but stillcontinue to be flexible.

[0030]FIG. 4 provides an exploded view of a form of the pump illustratedin FIG. 2. Accordingly, like elements carry the same reference numerals.

[0031] As illustrated, the pump housing is formed in two parts being apump body 20 and a drive cylinder 21. An elongate slot 22 is formedlongitudinally in the pump body 20 for receiving the pinch member 16.Extending from the pinch element 16 is a shaft 23 which engages throughbore 24 in the drive cylinder 21. Cap screws 25 are engagable throughopenings 26 in the pump body to screw into tapped openings (not shown)in the end of the drive cylinder 21 to combine the pump body 20 anddrive cylinder 21 together.

[0032] The distal end of shaft 23 engages into a spigot 27 extendingfrom piston 13. O rings 28 and 13 b are fitted to spigot 27 and andpiston 13 to provide a seal in bore 24 and cylinder 21 as the piston 13moves back and forth within the piston chamber 15.

[0033] A printed circuit board assembly 31 is fitted to the end of thedrive cylinder 21 by screws 30.

[0034] A microprocessor on this printed circuit board reads the positionof the vacuum piston 13 via opto couplers and accordingly the operationof solenoid valve 32.

[0035] The solenoid valve 32 is fitted to a threaded opening 33 in theside wall of the drive cylinder 21 via a coupling 34 and O rings 35.

[0036] In this form of the invention the valves and 18 and 18 a aremounted directly to the respective ends of the pump body 20. The inletvalve 20 comprises an inlet valve cover 36 which fits directly to theend of the pump body 20 there being a spigot 37 which engages into theend of the tube 12 within the tunnel 14. An inlet valve body 38 withvalve band 39 engages into the inlet valve cover 36 and the wholeassembly is fastened in place by cap screws 40 which engage through thevalve body 38 and valve cover 36 into threaded openings (not shown) inthe end of pump body 20. An inlet connector 41 with half nut 42 andclamp nut 43 are provided for coupling the pump to an inlet conduit.

[0037] Likewise, the outlet valve is provided by a valve body 38 a whichis mounted directly to the end of the pump body 20. An outlet valvecover 36 a and valve band 39 a are assembled together with the outletvalve body 38 a by cap screws 40 a.

[0038]FIG. 4 of the drawings, therefore, illustrates a practicalcommercial construction of a pump assembly using the “inflex” action ofthe pinch mechanism of the present invention.

[0039] As previously indicated, the tube is preferably of a flexiblesilicone type which is generally found to be long lasting and resistantto most types of fluids which could be expected to flow therethrough.

[0040] The pinch mechanism housing and ‘piston’ arrangement are mostsuitably constructed from hard-wearing plastic material. The housing maybe formed in a number of parts as efficient production requires andseveral external appearances are possible.

[0041] The invention is open to modification as will be apparent tothose skilled in the art. For example, the elongate pusher element 16 ofthe arrangement shown in FIGS. 2 and 4 could be replaced by a pluralityof pushers of the type shown in FIG. 1. The plurality of pushers wouldbe located side by side.

[0042] Also, the valves shown in the pump assembly of FIG. 2 or FIG. 4could be provided by a pinch mechanism of the type shown in FIG. 1. Theplungers could then all be linked to one motive force, eg via cams. Thishas the advantage of no valve being present in the product flow passageas all valve mechanisms would be external to the tube 12.

[0043] While in the drawings the tube 12 has been illustrated as beingof round cross-section, other cross-sectional configurations could beused such as an oval tube.

[0044] The pump assembly as disclosed herein and incorporating the pinchmechanism of the present invention can readily provide an on-demanddevice without the need for diverter valves and bleeds.

[0045] The improved pinch mechanism according to the present inventionthus provides a construction which allows accurate control over valveand/or pumping systems and may be used in many applications.

1. A pinch mechanism comprising a housing (11), an elongate flexibleconduit element (12) at least a part of which is located within thehousing, the conduit element providing a flow passage through which afluid flow can occur, and a conduit engagement means (13 c), theengagement means (13 c) having an engagement portion (13 d) with a crosssectional dimension less than a lateral dimension of the elongateconduit element (12) whereby the engagement portion is engageable withthe conduit element to restrict the flow passage and thereby limit fluidflow therethrough.
 2. A pinch mechanism comprising a housing (11), anelongate flexible conduit element (12) at least a part of which islocated within the housing, the conduit element providing a flow passagethrough which a fluid flow can occur, and a conduit engagement means (13c), the engagement means (13 c) having an engagement portion adapted tobe engageable with the conduit element, the engagement portion having across sectional dimension less than a lateral dimension of the elongateconduit element (12), wherein said at least part of said elongateconduit element (12) being constrained within said housing (11) to limitlateral movement thereof when the engagement portion engages with theconduit element to deform the conduit element to thereby restrict theflow passage.
 3. A pinch mechanism as claimed in claim 1 or 2 whereinthe conduit element is tubular and of circular cross section.
 4. A pinchmechanism as claimed in claim 1 or 2 wherein the conduit element (12) isof substantially elliptical shape with the lateral axis being the majoraxis of the elliptical shape.
 5. A pinch mechanism as claimed in any oneof claims 1 to 4 wherein the conduit element (12) is a flexible siliconetube.
 6. A pinch mechanism as claimed in any one of claims 1 to 5wherein the conduit element is resilient.
 7. A pinch mechanism asclaimed in any one of the preceding claims further including movingmeans (13) for moving the engagement means (13 c).
 8. A pinch mechanismas claimed in claim 7 wherein the moving means (13) is a piston (13 a)mounted for reciprocating movement in a piston housing (15) and furtherincluding pressure control means for controlling a pressure to thepiston (13 a).
 9. A pinch mechanism as claimed in claim 8 wherein thepressure control means includes a solenoid valve (32) coupling thepiston housing (15) to a pressure source.
 10. A pinch mechanism asclaimed in any one of claims 1 to 9 wherein the housing (11) includesconduit receiving means (14) in which said conduit (12) is located. 11.A pinch mechanism as claimed in claim 10 wherein the conduit receivingmeans (14) is a tunnel having a cross-sectional shape commensurate withbut slightly larger than the external cross-sectional shape of theconduit (12).
 12. A pinch mechanism as claimed in claim 10 or 11 whereinthe housing (11) has a passageway in which said engagement means (13 c)is slidingly engaged.
 13. A pinch mechanism as claimed in any one of thepreceding claims in which the engagement portion (13 d) has a curvedsurface, the diameter of which is equal to the external diameter of theconduit element (12) minus substantially four times the wall thicknessof the conduit element in the area of the conduit element where theengagement portion (13 d) contacts the conduit element.
 14. A pinchmechanism as claimed in claim 11 wherein the conduit receiving means(14) restrains the conduit element (12) against any significant lateralbulging.
 15. A pump including a pinch mechanism as claimed in any one ofthe preceding claims.
 16. A pump including a plurality of the pinchmechanism as claimed in any one of the preceding claims.
 17. A pump asclaimed in claim 15 or 16 wherein the or one of the engagement portion(13 d) is elongate having a longitudinal axis parallel to thelongitudinal axis of the conduit (12).
 18. A pump as claimed in any oneof claims 15 to 17 wherein to one side of the conduit (12) is provided anon-return inlet valve means (18) and to the other side of the conduit(12) is provided a non-return outlet valve means (18 a).
 19. A pump asclaimed in claim 18 wherein one or both of the valve means (18 and 18 a)is formed by a pinch mechanism of the type as claimed in any one ofclaims 1 to
 14. 20. A pump as claimed in claim 18 or 19 wherein theelongate conduit (12) is located with a pump body (20) which forms theconduit housing (14) and is retained therein by the valve means (18 and18 a) mounted to the body (20).